Step 1Blanch the snow pea leaves: Bring a pot of water to a boil. Add the leaves and blanch just to bring out the color, then drain immediately. Shock the leaves in a bowl of ice water to stop the cooking process and chill, then drain well. Finely chop the leaves and set aside.
Step 2Heat a large saute pan over medium-high heat until hot. Add the sesame oil, then stir in the mushrooms and water chestnuts. Cook until softened, 3 to 5 minutes, stirring frequently. Stir in the sugar, salt and mushroom broth, then remove from heat. Strain well to remove any excess liquid, then cover and refrigerate until chilled. Fold the chopped leaves into the chilled filling.
Step 3While the filling is chilling, make the dough for the wrappers: In a small bowl, whisk together the wheat and potato starches. Quickly pour in the boiling water, stirring it into the starches to form the dough. Quickly knead with your hands to moisten all the flour and work the dough until it is smooth and firm but cohesive (sprinkle over a little extra water, only if needed, to completely moisten the starch to form the dough).
Step 4Roll the dough into a log one-half-inch thick, then cut the log into one-half-inch pieces.
Step 5Working with one piece at a time (keep the rest covered with plastic wrap to prevent them from drying out), flatten it into a circle. Roll the piece (this is easiest using an Asian dowel-style rolling pin), into a 3-inch round, very thin wrapper. Use one hand to roll the dowel back and forth, while the other hand rotates the circle, like a steering wheel, to form the wrapper.
Step 6Place 1 rounded tablespoon of filling into the center of the wrapper. Moisten the outer edges of the wrapper, then gently fold over to enclose and form the dumpling into a desired shape. Repeat with the remaining dough, forming and filling the wrappers to make dumplings until you have about 3 dozen. Cover the dumplings loosely with plastic wrap until all are formed.
Step 7Prepare a bamboo steamer over a wok, or a steamer insert over a pot of boiling water. Place the dumplings in the steamer (to keep them from sticking, lightly oil the steamer bottom); the dumplings will need to be cooked in batches. Cover and steam until the dough is cooked and springy to the touch, 3 to 5 minutes.
Step 8Remove and repeat until all of the dumplings are steamed.